1. Field of the Invention
This invention relates to a semiconductor laser beam source apparatus used for a light beam scanning apparatus. This invention particularly relates to a semiconductor laser beam source apparatus wherein laser beams emitted by a plurality of semiconductor lasers are coalesced on an object to get a multiplied power of the laser beams on the object.
2. Description of the Prior Art
Light beam scanning apparatuses wherein a light beam is deflected and scanned by a light deflector have heretofore been widely used, for example, in scanning recording apparatuses and scanning read-out apparatuses. As one of the means for generating a light beam in the light beam scanning apparatuses, a semiconductor laser is used. The semiconductor laser has various advantages over a gas laser or the like in that the semiconductor laser is small, cheap and consumes little power, and that the laser beam can be modulated directly by changing the drive current.
However, the output of the semiconductor laser is low (20 mW to 30 mW) when oscillation is conducted continuously. Therefore, the semiconductor laser is not suitable for use in a light beam scanning apparatus wherein a scanning light beam of high energy is necessary, for example, a scanning recording apparatus for recording an image on a recording material having low sensitivity such as a draw material (metal film, amorphous film, or the like).
On the other hand, when certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a stimulable phosphor sheet provided with a layer of the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as a photographic film or on a display device such as a cathode ray tube (CRT).
In the aforesaid radiation image recording and reproducing system, it is desired to use a light beam scanning apparatus using a semiconductor laser for reading out the radiation image stored on the stimulable phosphor sheet by scanning the sheet. However, in order to cause the stimulable phosphor sheet to emit light in proportion to the stored radiation energy, it is necessary to expose the stimulable phosphor sheet to .stimulating rays having a sufficiently high level of energy. Accordingly, it is not always possible to use a light beam scanning apparatus using a semiconductor laser for image read-out in the radiation image recording and reproducing system.
In order to obtain a scanning laser beam of sufficiently high energy from the semiconductor laser of low light output, a plurality of semiconductor lasers may be used, and the laser beams emitted by the semiconductor lasers may be coalesced. One such semiconductor laser beam source apparatus for coalescing a plurality of laser beams is disclosed in Japanese Patent Application No. 59(1984)-121089. In this apparatus, the semiconductor lasers are positioned so that the optical axes of the laser beams are parallel to each other, and laser beams are converted into parallel rays by collimator lenses and then converged to a common spot by a converging lens.
In the aforesaid semiconductor laser beam source apparatus, in order to prevent the converging lens and the light deflector from becoming large and to minimize adverse effects of aberration of the converging lens, it is desired that the laser beams be as close to each other as possible when they impinge upon the converging lens. However, the general semiconductor laser which is available commercially has a large case, and it is not always possible to make the laser beams sufficiently close to each other. FIG. 4 is a perspective view showing an example of a proposed semiconductor laser beam source apparatus. In the apparatus of FIG. 4, in order to avoid the aforesaid problem, laser beams 31, 32, 33 and 34 emitted respectively by semiconductor lasers 11, 12, 13 and 14 and converted by collimator lenses 21, 22, 23 and 24 into parallel rays are reflected by reflecting mirrors 41, 42, 43 and 44 positioned so that their reflecting surfaces are parallel to each other. In this manner, large spaces are maintained between the semiconductor lasers 11, 12, 13 and 14, and the spaces between the laser beams 31, 32, 33 and 34 impinging upon a light deflector 5 and a converging lens 6 are decreased. The laser beams 31, 32, 33 and 34 made close to each other are deflected by the light deflector 5 constituted by a galvanometer mirror or the like and converged by the converging lens 6 to a spot S to scan on a scanning surface 7.
However, when the reflecting mirrors 41, 42, 43 and 44 are positioned to correspond to the laser beams 31, 32, 33 and 34 as described above, the directions of the reflecting surfaces of the reflecting mirrors 41, 42, 43 and 44 must be strictly adjusted so that the laser beams 31, 32, 33 and 34 are accurately parallel to each other when impinging upon the converging lens 6. The adjustment is not always possible to achieve.